A Study of Standard Methods for the Detection of Coliform Organisms in Raw and Treated Waters

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Abstract
Samples of untreated water, of plant effluents and of waters from selected points in the distribution systems were collected once a week for a full year from 3 water supplies. Samples were examined by strict adherence to Standard Methods. Detailed studies of coliform types isolated from the untreated surface waters derived from watersheds relatively unpolluted but graded in sanitary quality failed to yield significantly greater information than did determinations of total coliform densities by strict adherence to Standard Methods through the "completed test." Coliforms detected in "delivered" waters (from distribution systems free from cross-connections) frequently if not always reflect inadequacies of treatment which may have occurred at least as long as 3 weeks before the sampling date. This suggests that examination of samples from a distribution system may produce more useful results than inspection of plant records or examination of samples of plant effluent when water supplies are suspected of having caused gastrointestinal disturbances. The typing of coliform organisms found in a distribution system of the types studied is a matter of little importance. Their presence regardless of origin is a matter of concern directly proportional to the pollutional load of the untreated surface supply. Deviation from Standard Methods by overlooking atypical colonies and ignoring early or weak gas production in presumptive tests would result in failure to include a significant number of coliforms which show no evidence in pure culture of being degraded in lactose-splitting power and are frequently types of fecal origin. The adoption of standards for judging the safety of a supply over a period of time should be preceded by careful consideration of sampling points and of spacing of samples. Distinction should be made between "finished" water (plant effluent) as a means of judging the adequacy of treatment at the time of sampling and "delivered" water from selected points in the distribution system as a means of detecting past inadequacies of treatment. An arbitrary standard applied indiscriminately to all samples regardless of source and intervals between samplings may give an entirely false picture of plant opefation over a given period. This is true of the present "U. S. Treasury Department Standard" and explains why some believe it too strict and others too lax.

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